Endurance vs Interval Training

For decades, most experts and public health agencies have advocated moderate intensity, long duration exercise to improve health and maintain body weight. Despite that, more Americans are overweight or obese than ever. And, cardiovascular disease is the leading killer of Americans. Recently the Institutes of Medicine issued new recommendations urging all Americans to increase the duration of their exercise to at least one hour every day. It is as if you are being told that all your health problems could be solved and your heart made stronger if you could only overcome your laziness and make yourself do enough of that boring drudgery.

One small detail that is overlooked is the number of “well conditioned” endurance runners that die suddenly at the heights of their careers. In the 1970’s, Jimm Fixx claimed that the secret to heart health and long life was endurance running – up until he died of a heart attack – while running. In the 1980’s, Jack Kelly (husband of grace Kelly) went out for his usual morning run and, shortly after, dropped dead of sudden heart failure. At the time, he was the president of the US Olympic Committee.

Esimates from the American College of Cardiology’s 58th Annual Scientific Session showed the death rate for marathons was 0.8 per 100,000 participants. Even if uncommon statistically, if you’re the one, it is 100% for you. Just last year in the 2009 Detroit marathon 3 runners, aged 36, 65 and 26, collapsed and died suddenly toward the end of a half marathon.[1] We shouldn’t forget what happened at the first ever marathon: Phidippides ran 26.2 miles from marathon to Athens to report on the victory of the Greeks over the invading Persians. When he arrived, he announced “Nike!” which means victory, then collapsed and died. Is that really the model we want to emulate?

Undoubtedly endurance running makes your heart more efficient, evidenced by the lower resting heart rate of well-trained athletes, but may impair its reserve capacity. That is, the portion of its maximal output not used during routine activity. Trading reserve capacity for greater efficiency at continuous duration may not be what you want. Hear attacks do not occur for lack of endurance. They occur when there is a sudden increase in cardiac demand that exceeds the heart’s capacity to supply blood and oxygen, such as heavy physical exertion, sex, shoveling snow or suddenly encountering unusual stress.

A growing body of information reveals the varied detrimental effects of prolonged endurance exercise. A study from Massachusetts General Hospital documented elevated markers of cardiac damage in runners following a marathon.[2] Troponin, a protein found in cardiac cells and is a marker of cardiac damage was measured. It is also used in emergency departments to determine whether heart damage occurred during a heart attack. The runners all had normal cardiac function and no signs of troponin prior to the race. Shortly after completing the event, 60% of the runners had elevated troponin levels; 40% high enough to indicate destruction of heart muscle cells.

Another study documented increased inflammatory markers and markers of cardiac damage persisting more than 24 hours following a marathon.[3] Several studies have also revealed that marathon runners have reduced bone mass[4] Another study of male long-distance runners showed that they had lower levels of testosterone and higher levels of the stress hormone cortisol, and that these levels did not return to normal after a break in training.[5]

It is becoming clear that the real key to losing body fat, maintaining body composition and strengthening your heart is to exercise in shorter bursts at a higher intensity.

Patients who’ve had coronary artery bypass graft (CABG) surgery were found to get more long-term cardiac benefit from higher intensity aerobic interval training than from moderate continuous training. In a recent Norwegian study, VO2 peak improved significantly between baseline and week 4 in the aerobic interval group (27.1 versus 30.4 mL/kg-1/min-1; p < 0.001). VO2 peak also improved with moderate continuous training (26.2 versus 28.5 mL/kg-1/min-1), but not to a statistically significant extent. Between 4 weeks and 6 months, VO2 peak continued to improve in the aerobic interval training group, from 30.4 to 32.2 mL/kg-1/min-1 (p < 0.001). Again, the change in the moderate training group did not reach statistical significance (28.5 versus 29.5 mL/kg-1/min-1). In fact, these data show that the 4 week improvement in VO2 in the interval training group was greater than that achieved in the moderate continuous training group after 6 months.[6]

Research carried out at the Physical Activities Science lab in Québec, Canada compared high intensity interval training (HIIT) to moderate intensity endurance training.[7] The researchers calculated that the group doing long slow distance exercise burned more than twice as many calories while exercising than the group doing high intensity intervals. However, skinfold measurements showed that the HIIT group lost more subcutaneous fat. Even more interesting was the fact that when the difference in the total energy cost of the program was taken into account the subcutaneous fat loss was ninefold greater in the HIIT program than in the traditional long slow distance cardio program. What this means is the HIIT group got nine times more fat-loss benefit for every calorie burned exercising. Moderate intensity endurance exercise burns a higher percentage of fat during exercise. Compared to endurance exercise, high-intensity intermittent exercise causes more calories and fat to be burned following the workout. Would you prefer the gaunt, frail appearance of a marathoner’s body or the robust, muscular physique of a sprinter?

If you have health problems or are overweight and not used to exercise you do need to build a traditional aerobic cardio base first. However, sticking religiously to the same long slow distance program flies in the face of scientific evidence. Once you have your aerobic base it is time to make the step up to interval training. Providing the right exercise prescription, guidance and ongoing follow-up is imperative for safety and long-term success. Every individual is different.

At Alternity Healthcare, creating your customized program for exercise and lifestyle modification is based upon an intensive fitness assessment as well as other diagnostic information gathered during your full day Comprehensive Health Assessment: